Download the Digital Source & Printer Resolution Inter-dependence spreadsheet here:

Using the spreadsheet

Concepts:

This spreadsheet calculates the optimum print-sizes for a range of digital source media, including scanned traditional negatives, digital cameras and Kodak’s Photo-CD & Picture-CD systems. The word “optimum” is interpreted here as a print at the finest-possible resolution which contains every pixel in the source image, without discarding pixels or adding them by interpolation. In practise this means that each pixel in the digital source will correspond to an equivalent effective printer-pixel.

One of the most important aspects of printing photographs with inkjet or laser printers is understanding the difference between the printer’s quoted Maximum resolution and its Effective resolution. Most inkjet & laser printers can only emulate continuous tones by using dithered dot-clusters, the dimensions of which vary depending on the number of tones you require per effective printer-pixel. Few printer manufacturers quote the Effective resolution of their products when printing continuous-tone images. This spreadsheet attempts to calculate a printer’s Effective resolution from the printer’s hardware specification.

It’s important to note that the printer’s software driver and its setup have a significant influence on the end result - for example, many manufacturers employ Error Diffusion techniques in software to improve the perceived resolution. For this reason the spreadsheet includes a second set of Effective resolution figures to emulate error diffusion printer drivers.

No attempt has been made to accommodate printing technologies which vary ink-drop size to increase the number of available tones per dot - the number of different technologies and the wide range of capabilities make this impractical here. If you own such a printer, the optimum print-size will reduce, due to the smaller printer-dot cluster needed to emulate a large number of tones.

Entering data about your scanner & printer:

You’ll need to gather the following values from your scanner & printer’s hardware specifications, and enter the values into the thick-bordered boxes in the spreadsheet:

Scanner:

• Optical Resolution in Dots per Inch (default: 2700). If the manufacturer quotes different X & Y values, use the lower value. NEVER use the manufacturers’ interpolated resolution values
• Colour Depth in Bits (default: 24). This value is used to calculate the maximum number of tones the printer must support, and therefore the dimensions of the printed dot-cluster

Printer:

• Hardware Resolution in Dots per Inch (default: X=360, Y=720). Where the X & Y values are different, it is assumed that the printer uses this to increase the number of effective tones within a square printable dot
• Number of inks (default: 3)

Printer performance:

• Cell Width for Error-Diffusion drivers (default: 3)

Source Media:

• Dimensions of Custom film-size (if required)

That’s it. The calculation results can be seen in the “Printed Ouput” section of the spreadsheet.

Copyright © Timothy J. Baty 2002